The present invention relates generally to passenger loading bridges for transferring passengers between an aircraft and a terminal building, and more particularly to passenger loading bridges including a main elevating mechanism that is supplemented by a separate failsafe support mechanism.
In order to make aircraft passengers comfortable, and in order to transport them between an airport terminal building and an aircraft in such a way that they are protected from the weather and from other environmental influences, passenger loading bridges are used which can be telescopically extended and the height of which is adjustable. For instance, an apron drive bridge in present day use has a plurality of adjustable modules, including: a rotunda, a telescopic tunnel, a bubble section, a cab, and elevating columns with wheel carriage. Typically. one elevating column is mounted adjacent to each lateral surface of the telescopic tunnel. Manual, semi-automated and fully-automated alignment systems are known in the art for adjusting the position of the passenger loading bridge relative to an aircraft, for instance to compensate for different sized aircraft and to compensate for imprecise parking of an aircraft at an airport terminal. Of course, other types of bridges are known in the art, such as for instance nose loader bridges, pedestal bridges and over-the-wing (OTW) bridges.
The elevating columns are used to adjust the height of an outboard end of the passenger loading bridge so that the cab engages a doorway of each different type of aircraft at a proper height. After the cab is positioned to the proper height, the elevating columns are used to support the telescopic tunnel in such a way that an approximately level surface is maintained between the doorway of the aircraft and the cab of the passenger loading bridge. For example, as aircraft are loaded and unloaded with passengers, baggage, fuel and cargo, the aircraft raises and lowers on its undercarriage causing the height of the doorway to raise and lower. It is known to provide passenger loading bridges with automatic height adjustment or autolevel mechanisms which sense the vertical movement of the aircraft and automatically adjusts the height of the cab of the passenger loading bridge accordingly. As such, the elevating columns typically are activated from time to time, while the aircraft is being loaded and unloaded, in order to compensate for such vertical movement of the aircraft.
Each elevating column typically is provided with a separate mechanism for extending and retracting the length of the elevating column. The mechanism may be electrohydraulic, as where a motor drives a pump which supplies fluid to extend or retract a hydraulic cylinder which raises or lowers the outboard end of the bridge, or may be electromechanical, as where a motor drives an electromechanical screw which raises or lowers the outboard end of the bridge. In either case, the motor is responsive to a control signal for raising and lowering the outboard end of the bridge. For instance, a first control signal operates the motor in one direction and causes the mechanism to elevate the outboard end of the passenger bridge, and a second control signal reverses the motor and causes the mechanism to lower the outboard end of the passenger bridge.
It is a disadvantage of the electrohydraulic mechanism that a ruptured check-valve or a burst hydraulic fluid line could allow hydraulic fluid to escape from the system, either slowly or rapidly, with a corresponding loss of hydraulic pressure within the hydraulic system. As a result, the passageway of the bridge would begin to descend in an uncontrolled manner. It will be obvious to one of skill in the art that the uncontrolled descent of a passenger loading bridge could result in serious injuries to persons in and about the passenger bridge. There is also the risk of serious damage occurring to service equipment that is located beneath the passenger bridge, as well as to the aircraft that is being serviced by the passenger bridge at the time of the failure. Of course, the greatest potential for damage occurs with the use of OTW bridges, wherein an uncontrolled descent of the passenger bridge could allow a portion of the bridge to make contact with a wing of the aircraft, possibly rupturing one of the aircraft""s wing fuel tanks or fuel lines, thereby increasing the chance of an apron fire occurring.
Electromechanical screw mechanisms are also widely used in conjunction with the elevating columns of passenger loading bridges. Typically, the electromechanical screw mechanism is designed to operate rapidly so as to minimize the amount of time that is required to adjust the height of the passenger loading bridge for each different type of aircraft. Minimizing the amount of time that is required to adjust the height of the passenger loading bridge contributes to faster aircraft turn-around times, which provides a significant economic advantage to the airlines whose aircraft are capable of generating revenue only when they are in the air. The electromechanical screw mechanism is also designed to operate using the limited power resources that are available to each passenger loading bridge. To this end, often ball screws are employed comprising a semicircular groove machined into a xe2x80x9clead rodxe2x80x9d in which ball bearings run. The bearing housing allows the balls to recirculate, which provides a very smooth and efficient drive. This means that the elevating column can operate at very high speeds and loads for long periods without damage. Unfortunately, the weight of the passenger loading bridge often is sufficient to back-drive or xe2x80x9cwind downxe2x80x9d the ball screw mechanism. As a result, each electromechanical screw mechanism typically includes a ball screw that is coupled to a separate heavy-duty motor. Each heavy-duty motor includes an electromagnetic brake that engages when power to the motor is cut off, for instance during a power failure or absent a signal for controlling the motor. Since the brakes are relied upon to support the entire weight of the passenger loading bridge, there is a tendency for the lifting systems of passenger loading bridges to be xe2x80x9cover designedxe2x80x9d. For example, providing one heavy-duty motor with each electromechanical screw mechanism ensures redundancy, such that in the event that one of the heavy-duty motors fails, the remaining one will still support the entire weight of the bridge. This increases the complexity of the passenger loading bridge, resulting in increased capital costs and higher maintenance costs. Furthermore, in the event that one of the heavy-duty motors fails, there is no additional redundancy built into the system to prevent the uncontrolled descent of the passenger bridge.
Adding to the concern, there is a trend in modern passenger loading bridges to mount the 400 Hz power supply unit and the preconditioned air unit near the cab of the passenger loading bridge. These two units add approximately 10,000 pounds to the amount of weight that is being supported by the elevating columns. In the event of a failure of the elevating columns, this additional weight increases the downward force that is exerted by the passageway of the passenger loading bridge upon the elevating columns, as well as upon any objects that happen to be located beneath the passageway. If these units are added as a retrofit to the passenger loading bridge, then further modifications may also be required at that time to ensure that each one of the two heavy-duty motors is capable of supporting the combined weight of the bridge and the retrofitted units.
Of course, xe2x80x9csaferxe2x80x9d mechanisms are known that avoid some of the disadvantages associated with the above-mentioned mechanisms. An example of such a xe2x80x9csafexe2x80x9d mechanism is an electromechanical screw mechanism including a drive screw having an acme thread. The weight of the passenger loading bridge produces a downwardly directed force that is insufficient to back-drive such a xe2x80x9csafexe2x80x9d mechanism, and therefore the xe2x80x9csafexe2x80x9d mechanism is effectively sel-flocking or xe2x80x9cself-arrestingxe2x80x9d. That said, the efficiency of a drive screw having an acme thread is lower, typically 30-50% depending upon nut preload, compared to that of a ball screw. Accordingly, such a xe2x80x9csafexe2x80x9d mechanism operates more slowly and requires a greater amount of power compared to a typical electromechanical screw currently in use. This is especially true when the xe2x80x9csafexe2x80x9d mechanism is required to raise and lower a substantial amount of weight, such as for instance the weight of a passenger loading bridge. Furthermore, the reliability and life span of a drive screw having an acme thread are reduced under high load operating conditions. Other xe2x80x9csafexe2x80x9d mechanisms, such as for example a redundant ball-path screw, are subject to similar limitations. Accordingly, it is very difficult to implement an elevating column of a passenger loading bridge that includes a xe2x80x9csafexe2x80x9d mechanism. In fact, the use of a xe2x80x9csafexe2x80x9d mechanism is practical only when the mechanism is not required to raise or lower a substantial amount of weight. Of course, this critical condition is not satisfied in the prior art lift systems since the elevating columns usually bear a substantial portion of the weight of the passenger loading bridge under normal operating conditions.
It would be advantageous to provide a back-up mechanism that is separate from the main elevating columns, for supporting a passenger loading bridge in the event of a failure of the main lift system.
In order to overcome these and other limitations of the prior art, it is an object of the instant invention to provide a failsafe support for supporting a passenger loading bridge in the event of a failure of a main support.
In accordance with an aspect of the instant invention there is provided a failsafe support for a passenger loading bridge having a passageway that is supported in a height-adjustable manner by a main support including at least a height-adjustable support post, the failsafe support comprising: a support portion for being positioned adjacent to a lower surface of a passenger loading bridge passageway in a first operating condition and for engaging the lower surface of the passenger loading bridge passageway in a second operating condition; a height-adjusting portion extending from the support portion to a mounting end, the mounting end for being mounted to the main support; and, a self-arresting mechanism for varying at least one of a length of the height-adjusting portion and an orientation of the height-adjusting portion in the first operating condition and for maintaining approximately constant the at least one of a length of the height-adjusting portion and an orientation of the height-adjusting portion in the second operating condition, wherein the failsafe support supports a weight that is significantly less than an entire weight of the passenger loading bridge passageway when in the first operating condition, and wherein the failsafe support bears a substantial portion of the weight of the passenger loading bridge passageway when in the second operating condition.
In accordance with another aspect of the instant invention there is provided an apparatus for supporting a passageway of a passenger loading bridge in a height-adjustable manner, comprising: a main support, including: a wheeled frame; and, a lift mechanism having a first end and a second end opposite the first end, the lift mechanism mounted to the wheeled frame at the first end and mounted to a passageway of a passenger loading bridge at the second end, for supporting the passageway of the passenger loading bridge in a height adjustable manner; and, a failsafe support having a support end and a height-adjusting end, the failsafe support mounted at the height-adjusting end to the wheeled frame of the main support such that, in use, the support end is positionable adjacent to a lower surface of the passageway of the passenger loading bridge being supported by the lift mechanism of the main support, wherein the failsafe support maintains the passageway of the passenger loading bridge at approximately a height of the support end in the event of a failure of the lift mechanism of the main support.
In accordance with yet another aspect of the instant invention there is provided a kit for retrofitting a passenger loading bridge equipped with a main support member including at least a height-adjustable lift mechanism, the kit comprising: a failsafe support member having a mounting portion adapted to be mounted to a frame of a main support member and a support portion for supporting the passenger loading bridge, the failsafe support member including a self-arresting mechanism for varying a distance between the mounting portion and the support portion; and, a motor for providing to the self-arresting mechanism a sufficient amount of power for varying the distance between the mounting portion and the support portion when the failsafe support is other than supporting a weight of the passenger loading bridge.